1. Field of the Invention
The invention relates to a device for continuously mixing fed-out natural gas with oxygen to produce a burnable gas for heating the pressurised natural gas before or after the relaxation thereof, with a closed mixing container with connection for a natural gas supply line, an oxygen in-feed line and a burnable gas discharge line.
2. The Prior Art
On removal from storage, e.g. from underground storage tanks, natural gas must be preheated before its pressure is reduced in order to compensate for the Joule-Thomson effect. The continuous burning of part of the removal flow in a so-called “in-line reactor” with the controlled supply oxygen is known. In this method, through the catalytic conversion of oxygen with natural gas, temperatures of up to 400° C. are reached directly in the gas flow being removed from the store. The heat is used for continuous heating through directly mixing the hot combustion gas into the cold gas flow. This method is described in EP 0 920 578 B1.
It has been shown that self-ignition of the gas mixture during the process of supplying oxygen to the natural can never be entirely ruled out. The self-ignition of natural gas-oxygen mixtures is dependent on pressure and temperature. Even without a catalyst an increased oxygen content is enough to result in a reaction and combustion in the gas flow, and therefore in an increase in pressure and temperature. In the real technical conditions of a natural gas withdrawal plant, with the currently known and available measuring and control technology and in connection with the safety measures that can be implemented with currently known means, the supplying of oxygen to natural gas by means of a burner, diffusion burner or a premixing chamber as described in EP 0 920 578 cannot be controlled with certainty.
In view of the high temperatures arising during direct ignition at the oxygen discharge point, the free flowing in of oxygen into the natural gas flow is not recommended. Furthermore the use of known ignition and monitoring devices will fail after a very short period of time.
On the other hand it has been shown that “cold” adding of oxygen to the natural gas for an exothermic reaction on a Catalyst is not successful. The preheating of the natural gas-oxygen mixture to the activation temperature of the catalyst with the concentration remaining the same before relaxation regularly leads to uncontrollable self-ignition and consequently not to the required catalytic conversion of the mixture of natural gas and oxygen.